Increasingly, driver assistance systems are used in vehicles, which support the driver in keeping the vehicle on the lane. Assistance systems, which warn the driver when unintentionally departing the vehicle lane are called in English Lane-Departure Warning Systems (LDWS). Systems, which can directly intervene in the steering, are called in English Lane Keeping Systems (LKS). In German, these systems generally are referred to as a lane keeping assistance systems.
Lane keeping assistance systems are usually in the position to detect the lane in front of a vehicle (so-called lane detection), thus in particular the road course. Particularly, the lane keeping assistance systems estimate the lane width, the horizontal and/or vertical road curvature, the offset from the lane center as well as the pitch and yaw angle of the vehicle. From these system parameters, the time until departure of the lane can be calculated, and the driver can be warned of an unintended departure of the lane or the vehicle can be kept in lane with the aid of an electric steering or a specific ESP-intervention (Electronic Stability Program).
The above system dimensions can be determined in particular by a digital image processing of the position in front of the vehicle detected by an optical sensor, for example a CMOS camera. For this purpose, a special image processing algorithm is used, which evaluates structures in the detected images, which are characteristic of a vehicle lane and its course, for example road markings or boundaries of a road such as guardrails and the like. The correct functioning of a lane keeping assistance system based on such an image processing depends mainly on the fact that in the detected digital images the structures essential for the lane detection are detected reliably and accurately. The used image processing algorithm detects markings mainly as a result of dark-bright/bright-dark transitions between the road and lane markings. Further, the images are searched for structures with the highest contrast, since these are mostly generated by said transitions. If, however, in the images structures with a high contrast appear, which are not generated by lane markings, this may lead to the fact that the image processing algorithms either does not correctly detect a lane, or is not in a position at all to detect a lane. EP 1320072 A2, which is incorporated by reference, discloses a method for detecting lane markings, wherein from an image edges with the corresponding angle are extracted. Further, those edges are extracted, which are aligned to a vanishing point. From this edges lane markings are determined.